This invention relates to combined heat pump and hot water systems that provide heating of an indoor air space, cooling of the indoor air space, and heating of domestic water, with or without heating or cooling.
Integrated heat pump systems of this type have a compressor and indoor and outdoor heat exchanger coils, and a water heat exchanger. Compressed refrigerant flows through the water heat exchanger and gives up superheat to water in the heat exchanger. Then the compressed refrigerant vapor flows via a reversing valve to either the indoor coil (for heating mode) or to the outdoor coil (for a cooling mode). From there the refrigerant proceeds as condensed liquid to the other of the heat exchanger coils, where it passes through an expansion device into the coil, where the compressed refrigerant evaporates and picks up heat. Hot water is provided in either a cooling mode or a heating mode.
Where neither space heating nor cooling is called for, the system can still provide water heating and the water heat exchanger rejects the bulk of the refrigerant heat into the water. In that case, the heat exchanger fan associated with the condenser coil is kept off, but that of the evaporator coil is actuated on. For example, when the reversing valve is set for a heating mode, but space heating is not called for, the indoor fan is not run. On the other hand, when the reversing valve is set for cooling, but cooling is not called for, the outdoor fan is not run. Both superheat and condensing heat are rejected into the water.
The water heat exchanger is rather small in heat transfer capacity relative to the indoor air heat exchanger or the outdoor air heat exchanger. Therefore, when the water heat exchanger serves as the sole or principal refrigerant condenser, as it does during a dedicated water heating cycle when neither heating nor cooling is called for, the heat exchange capacity of the system is unbalanced and no longer matches the pumping capacity of the compressor. Thus, it is necessary somehow to reduce the effective pumping capacity of the compressor when the evaporator coil is generating high pressure due to high air temperatures. One technique to accomplish this is discussed in my earlier U.S. Pat. No. 4,727,727. Another technique involves artificially reducing the compressor suction-pressure by using a regulator or valve in advance of the suction port.
These techniques tend to be rather complex to implement, or can reduce rather than enhance the system efficiency.
The industry has long sought a simple, cost effective way to match compressor efficiency to capacity of the water heat exchanger during times when hot water is demanded, but neither space heating nor space cooling is required.